Can anyone design me a lilliput regullator?

voodoocreations · 02-14-2004, 12:34 PM

Hello.
Can anyone design me a regullator for the lilliput lcd display?
Thank you.

shchua · 02-15-2004, 07:05 AM

I'm building one right now. I'm using a LM2577 switching regulator in boost mode to convert 8-14V to 16V, then regulating it down to 12.6V (adjustable) using a LM317T. The 12.6V is to allow for voltage drop in the cable to the Lilliput and for more brightness.

The LM2577 circuit is the same one in the NS data sheets (using a 100 uH inductor) and the LM317T part is also another no brainer.

masch · 02-16-2004, 02:01 AM

That is a great idea shchua.. but what is NS?

btw, why dont you guys just use the DC regulator supplied with the LCD?

shchua · 02-16-2004, 07:48 AM

Quote: Originally Posted by masch

That is a great idea shchua.. but what is NS?

btw, why dont you guys just use the DC regulator supplied with the LCD?

The regulator (egg shaped thingy) that came with my Lilliput has a dropout voltage of about 1.7V. When the engine is running, this is not a problem since the battery voltage is about 13.8V so the regulator's output is a nice solid 12V. When I turn off the engine, the battery voltage drops to about 12.8V causing the regulator output to drop to 11.1V. On my Lilliput, the brightness drops significantly which I dislike. I switched to using the +12V output from my Opus 150 but the problem is that the actual voltage at the Opus is 11.86V (non-adjustable according to Kris) and that drops to about 11.5V by the time it reaches the Lilliput.

I've been running the Lilliput at 12.6V using my new regulator and its fine so far. It appears that the Lilliput will work down to about 10.8V with significant reduction in brightness so I'm thinking of varying the supply voltage to reduce the brightness at night.

I'll recycle the Lilliput regulator (change one resistor) to produce 5V output for my USB hub.

slffl · 05-21-2004, 02:22 PM

So the Opus doesn't provide a solid 12v? Oh man, I just fried my egg regulator and was planning on powering my lilliput through the opus, but I don't want a dim screen.

Are there any other alternatives? Are there 12v regulators available for purchase anywhere?

pugstyle · 05-22-2004, 08:55 AM

Quote: Originally Posted by shchua

I'm building one right now. I'm using a LM2577 switching regulator in boost mode to convert 8-14V to 16V, then regulating it down to 12.6V (adjustable) using a LM317T. The 12.6V is to allow for voltage drop in the cable to the Lilliput and for more brightness.

The LM2577 circuit is the same one in the NS data sheets (using a 100 uH inductor) and the LM317T part is also another no brainer.

can you put at pic down or a pcb so we can se how you will conect it

Pokey · 05-22-2004, 09:06 AM

quote "convert 8-14V to 16V, then regulating it down to 12.6V"

Could i ask what you gain by doing this? Seems inefficient to me, I mean a LM2577 is a regulator isnt it?

scsirob · 05-22-2004, 10:31 AM

Most converters including the LM2577 can only convert up or down, not both. When your desired output is 12V and the input can be either above or below you have two options:
- Do it in two steps like shchua does
- Build something which involves flyback transformers, which are usually expensive and hard to get if you don't want to order 1000+ of them.

Using two steps can be reasonably efficient and still cheap.

shchua · 05-22-2004, 10:35 AM

Quote: Originally Posted by Pokey

quote "convert 8-14V to 16V, then regulating it down to 12.6V"

Could i ask what you gain by doing this? Seems inefficient to me, I mean a LM2577 is a regulator isnt it?

Yes, but a LM2577 has a dropout voltage of about 1.5V. The battery voltage drops to about 12.6V when the engine is off, so the output voltage will drop to (12.6 - 1.5) or 11.1V. This causes the brightness of the Lilliput to dim noticeably.

By boosting to 16V, then regulating down to 12.6V, I get a nice bright display whether the engine is on or off. As for the circuit diagram, I used the one straight from the National Semiconductor data sheets for the LM2577 - the inductor value used is 68 uH. This is followed by a LM317T linear regulator with R2/R1 ratio set for 12.6V output.

If you don't mind having a dimmer display when the engine is off, you can omit the LM317T and configure the LM2577 for 12.6V output.

Scouse Monkey · 05-23-2004, 04:33 AM

Hi, could you post links to or info where you get the data sheets you are using to build this.

Cheers

Curiosity · 05-23-2004, 12:50 PM

Would there be an easy way to adjust it based on a photoresistor? You know where I'm going with this, right?

pugstyle · 05-23-2004, 02:32 PM

Quote: Originally Posted by shchua

As for the circuit diagram, I used the one straight from the National Semiconductor data sheets for the LM2577 - the inductor value used is 68 uH. This is followed by a LM317T linear regulator with R2/R1 ratio set for 12.6V output.

i now i sound stupid but could jo post a pic for me i'm best with visual things

plus these parts you are using i don't think i can get it were i live so i maby have 2 use some other parts. i hope it's not to much

shchua · 05-24-2004, 03:08 AM

Quote: Originally Posted by pugstyle

i now i sound stupid but could jo post a pic for me i'm best with visual things

plus these parts you are using i don't think i can get it were i live so i maby have 2 use some other parts. i hope it's not to much

OK, here's the diagram. The LM2577, LM317T and 1N5821 are fairly easy to get. I had problems getting the correct inductor (68 uH, 3A) but managed to find one that was fairly close after scrounging around. Hope this helps.

MrPerfectionest · 05-24-2004, 05:44 AM

This is a pretty good way for a casual hobbyist to accomplish this problem as part count is low and not too complex. Since you aren't dropping too much voltage then heat isn't a problem with the LM317, you could probably surface mount it to a copper plane and have enough heat sinking.

djg · 05-24-2004, 01:40 PM

Here's a link to a commercial DC-DC converter with a 2.1 A, 12 VDC output with an input range of 9 to 18 VDC:
http://www.astrodyne.com/pdf/SD25.pdf

The price is shown as $41. in single unit quantities. I have not tried one of these yet but plan to soon - The price seems cheap enough to avoid building it myself:
http://www.astrodyne.com/astro/produ..._id=6&watts=26

I am sure there are other companies offering similar products. These guys have a 5 A. model but it's a little pricey at over $100. but both are about $20./amp.

Dave